Detection of World War II field fortifications using ALS and archival aerial images – German OKH Stellung b1 trenches in the south of the Polish Carpathians

Abstract

AbstractThis article recreates the spatial distribution of German field fortifications in the mountains of Central Europe. The fortifications in question were located in the southern part of the Polish Carpathians. This particular section is a fragment of the Oberkommando des Heeres Stellung b1 (OKH Stellung b1), built in 1944, and running from north to south through all of German‐occupied Poland. Determining the course of the studied fortifications is based on the use of two remote sensing materials for data acquisition: archival military aerial photographs taken in 1944 and high‐resolution terrain derivative models based on data from airborne laser scanning (ALS). Some sections were additionally checked during the field study.Creating a reconstruction is impossible without the use of both remote sensing data sources. Only 24% of the studied fortifications are visible in both the aerial photographs and the ALS model. Aerial photographs are better suited to the photointerpretation of trenches in arable land and near buildings. Objects in these places may have been buried or otherwise ceased to be visible as relief microforms. The ALS model is especially useful in wooded areas. Laser scanning with a large number of measurements enabled the implementation of a detailed model which also included the course of trenches under the tree canopy. Combining both source materials gave a spatial image of approximately a 30 km section of the fortified line. The total length of the fortifications was 85.412 km. The reconstructed line consists of two parallel trench lines with excavations for machine gun nests and shelters, as well as isolated points of defence located in the mountains near the current border.